Organic opto-electronic devices and method for making the same

ABSTRACT

The present invention pertains to new flip-chip organic opto-electronic structures and methods for making the same. The new organic opto-electronic device includes at least two separate parts. Each part comprises an electrode and at least one of these electrodes carries an organic stack. After completion of these separate parts both are brought together to form the complete opto-electronic device. It is a crucial aspect of the new flip-chip approach that spacers are integrated on one or both sides of the parts and that an interface formation process is employed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/368,153, filed Aug. 4, 1999 now U.S. Pat. No. 6,316,786, the contentsof which is expressly incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns new organic opto-electronic devices, suchas organic light emitting diodes (OLEDs), organic displays, organicsolar cells, photodiodes and the like. Also addressed is a new methodfor making such devices.

2. Discussion of the Related Art

Organic light emitting diodes (OLEDs) are an emerging technology withpotential applications as discrete light emitting devices, or as theactive elements of light emitting arrays, such as flat-panel displays.OLEDs are devices in which a stack of organic layers is sandwichedbetween two electrodes. At least one of these electrodes must betransparent in order for light—which is generated in the active regionof the organic stack—to escape. To achieve high efficiency and lowvoltage operation each of the organic layers as well as the electrodeshave to be optimized for their individual function; charge carrierinjection, charge carrier transport, charge carrier recombination, andlight extraction. Despite the great progress achieved in recent years,full optimization is difficult to obtain using conventional approaches,as will be outlined below.

OLEDs emit light which is generated by injection electroluminescence(EL). Organic EL at low efficiency was observed many years ago inmetal/organic/metal structures as, for example, reported in Pope et al.,Journal Chem. Phys., Vol. 38, 1963, pp. 2024, and in “RecombinationRadiation in Anthracene Crystals”, Helfrich et al., Physical ReviewLetters, Vol. 14, No. 7, 1965, pp. 229-231. Recent developments havebeen spurred largely by two reports of high efficiency organic EL. Theseare C. W. Tang et al., “Organic electroluminescent diodes”, AppliedPhysics Letters, Vol. 51, No. 12, 1987, pp. 913-915, and by a group fromCambridge University in Burroughes et al., Nature, Vol. 347, 1990, pp.539. Tang used vacuum deposition of molecular compounds to form OLEDswith two organic layers. Burroughes spin coated a polymer,poly(p-phenylenevinylene), to form a single-organic-layer OLED. Theadvances described by Tang and in subsequent work by N. Greenham et al.,Nature, Vol. 365, 1993, pp. 628-630, were achieved mainly throughimprovements in OLED design derived from the selection of appropriateorganic multilayers and electrode metals.

To date, virtually all OLED device structures have been built on glasssubstrates coated with indium-tin oxide (ITO), which serves as atransparent anode, i.e. light is emitted through the To anode andsubstrate. This kind of a device structure is usually referred to ascathode-up structure. The cathode is typically a low-workfunctionelemental metal or low-workfunction alloy, e.g. Ca, Al, Mg/Ag, or Al/Li.Such cathodes are opaque. These low-workfunction elemental metals andalloys belong to the first class of cathode materials considered forOLEDs.

In order to enable a variety of possible applications, OLED structuressuitable for opaque substrates (i.e. substrates other than theconventional glass substrates) are highly desirable. For example, ifOLEDs could be fabricated on silicon, this would permit the use of anintegrated active-matrix drive scheme. In such a structure light must beemitted through the uppermost layers of the device rather than throughthe substrate. One possible solution would be to build OLEDs bydepositing the layers in the opposite order, which means a structurewould be obtained with the transparent ITO anode deposited on top(referred to as anode-up structure). This has proved difficult,presumably due to the harsh conditions under which the ITO is deposited.

Alternatively, devices could be fabricated with the normal sequence oflayers provided that a transparent cathode could be found. GalliumNitride (GaN) has already been suggested as one possible cathodematerial for these kind of alternative cathode-up structures, asdisclosed and described in an international patent applicationW098/07202 with title “Gallium Nitride Based Cathodes for OrganicElectroluminescent Devices and Displays”. The international publicationdate of this patent application is Feb. 19, 1998. The GaN is anon-degenerate, wide-bandgap semiconductor (nd-WBS). As described in theinternational application, all nd-WBSs have the advantage that theirwide bandgap makes them transparent. It has been shown that the widebandgap also leads to a favorable alignment of either the conductionband or valance band with the lowest unoccupied molecular orbitals(LUMO) or highest occupied molecular orbital (HOMO) of the organicmaterial into which charge is to be injected. These non-degenerate,wide-bandgap semiconductors form a second class of cathode materialsconsidered for OLEDs.

It has been shown that improved performance can be achieved when theelectrode materials are chosen to match the respective molecularorbitals of the organic material into which it is supposed to injectcarriers. By choosing the optimized electrode materials the energybarriers to injection of carriers can be reduced.

It has been shown in U.S. Pat. No. 5,340,619, with title “Method ofmanufacturing a color filter array”, that ink-jet printing or otherprinting technologies can be used to coat a substrate. First, thesubstrate is coated with a blue resin which is baked (cured) before redand green colored polyimide dyes are each added and cured respectively.After all the colors are added and cured, laser ablation is used toreduce the thickness of the coating to develop a color filter array.

With multilayer device architectures now well understood and commonlyused, the major performance limitation of OLEDs is the lack of idealcontact electrodes, and in particular the lack of transparent andconducting materials which can be deposited on organic layers withoutcausing damage having a detrimental effect on the device performance andreliability.

One figure of merit for electrode materials is the position of theenergy levels (bands) relative to those of the organic materials. Insome applications it is also desirable for the electrode material to betransparent, as mentioned above. Furthermore, the electrode should bechemically inert and capable of forming a dense uniform film toeffectively encapsulate the OLED. It is also desirable that theelectrode and/or electrode deposition does not lead to a strongquenching of EL.

Another important figure of merit for electrode materials is the ease ofhandling and problem-free deposition on organic layers. Furthermore, theelectrode materials have to be compatible to the organic materialsunderneath which is often difficult to achieve.

The incompatibility problems inherent to most electrode materials usedso far can be extended and generalized. The most severe limitations inthe deposition of metals and semiconductor-based electrodes onto organiclayers are:

damage of the organic materials during the deposition which often leadsto irreversible changes within the organic layers and at theirinterfaces;

damage of the organic materials due to heat treatments required toobtain electrodes with good physical, mechanical and electrical andelectro-optical properties. High process temperatures lead to thermaldamage of the organic materials such as crystallization, interdiffusionand intermixing of the organics.

low manufacturing yield because the more processing steps are performed,the lower the output of fully functional devices gets.

reduced number of materials available, because not-only electrical, butalso chemical compatibility with the organic materials is required. Forexample, up to now no polymers can be deposited on top of evaporatedorganic layers, because of dissolving problems.

So far, there is a costly and time-consuming search for better suitedmaterials which may serve as stable, possibly transparent electrodes.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a new andimproved approach which allows to overcome some or all of theabove-mentioned problems and disadvantages.

It is an object of the present invention to provide new and improvedorganic opto-electronic devices such as organic light emitting devices,arrays and displays as well as solar cells and photodiodes.

It is another object of the present invention to provide a method forthe formation of new and improved organic opto-electronic devices suchas organic light emitting devices, arrays and displays as well as solarcells and photodiodes.

The above objects have been accomplished by providing new flip-chiporganic opto-electronic structures and methods for making the same.According to the present invention, the opto-electronic device includesat least of two separate parts. Each part comprises an electrode and atleast one of these electrodes carries an organic stack. After completionof these separate parts both are brought together forming the completeopto-electronic device. The interface between the two flip-chip partscan be stabilized by applying a special interface formation procedure.

It is a crucial aspect of the new flip-chip approach that spacers areintegrated on one or both sides of the parts. These spacers have to meetthe following criteria to ensure proper operation of an organicopto-electronic structure:

the size and shape of the spacers have to be such that sufficientelectrical contact is provided between the organic layers on thedifferent pieces or the organic layer and the electrode on the differentparts.

the spacers must prevent short circuits. This means that the spacersconsist either of non conducting materials or if they are conductingthey should be electrical isolated at least from one electrodestructure.

the spacers have to be rigid, to protect the organic layers from damage.This is especially important for flexible device structures.

the total thickness of the spacers have to be chosen in such a way, thatsufficient electrical contact between the organic layers is provided anddamage between the organic layers is avoided.

The inventive flip-chip approach allows to split off the devicefabrication process and therefore separates the respective incompatibleprocess steps. Both fabrication processes can thus be separately andindependently optimized.

It is an advantage of the present flip-chip approach that both theorganic structure and the electrode structure can be tested andinspected before putting them together.

The inventive approach capitalizes primarily on the inventor's findingthat a contact of sufficiently high quality can be obtained between theelectrode structure and the organic structure if the spacers aredesigned appropriately. It furthermore is based on the conclusionderived from experiments, that an organic opto-electronic device in factcan be put together using two separate and discrete parts, namely anorganic structure and a complementary electrode structure. It can evenbe more general, in that a structure is put together from two separateparts which both consist of an electrode structure and parts of theactive layers. The approach to fabricate an organic device in twoseparate parts is unique because experts currently working on organicdevices are in particular concerned about the quality of the interfacesbetween adjacent layers. Until now it seemed to be inconceivable—if noteven completely out of the question—to ‘take’ an organic device apart.Should the interface quality of a flip-chip device according to thepresent invention not be acceptable, one might employ a special heattreatment. Experiments showed that the quality of the interfaceformation can be adjusted or tailored by applying such a special heattreatment.

The inventive approach further capitalizes on the inventor's findingthat the interface between the two flip-chip parts can be stabilized, oroptimized, or tailored by applying a special interface formationprocedure.

The results of the experiments are very surprising in particular if oneconsiders them in the light of the existing prejudice.

It is also important to consider, that the inventive approach iscompletely foreign to conventional semiconductor technology where anelectrode or metalization always is formed right on the semiconductinglayers to ensure intimate contact.

Other advantages will become obvious form the detailed description andthe drawings.

In one embodiment of the present invention a first substrate carrieselectrodes only, whereas the second substrate carries an electrodetogether with the complete organic stack of one or more organicopto-electronic devices.

In another embodiment, the first substrate carries electrodes and partof the organic layers. The second substrate also carries some of theorganic layers and another electrode.

In yet another embodiment, the present flip-chip approach is used tomake an organic light emitting array, such as a display for example.

Employing a flip-chip technology in accordance with the presentinvention adds flexibility in the choice of electrode designs.

Some further advantages of the inventive approach are:

electrodes can be deposited at conditions otherwise not suited for OLEDformation (e.g. high temperature, aggressive chemical environment, iondamage (sputter damage), high energy particle processes);

electrodes can be easily patterned;

separate testing and inspection of both ‘halfs’ is possible. This helpsto increase the yield and thus reduces manufacturing costs.

each ‘half’ can be made of optimized materials and using optimizedprocesses without having to take care of incompatibility issues.

If appropriately designed, the spacers also serve as studs or postswhich protect the sensitive parts from being mechanically damaged duringhandling, as will be discussed in connection with FIGS. 1A and 1B.

The present approach is well suited for the formation of large areadisplays, for example, where the yield is one of the major cost factors.The larger an active matrix display gets, the more likely it is that onetransistor fails. In such a case the whole display is not suited for useand has to be discarded. The present approach leads to a drasticallyincreased yield which in turn allows to make cheaper display.

The spacers can provide conductive connection between circuitry on thetwo halves. This is especially important for large area displays wherethe conductivity of the common electrode limits the device performance.

Additional spacers can be employed that provide a conductive connectionbetween circuitry on the two ‘halfs’.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to thefollowing schematic drawings:

FIG. 1A is a schematic cross section of a first substrate carrying anelectrode (referred to as electrode structure) and a second substratecarrying an organic light emitting stack with a common electrode(referred to as organic structure), according to the present invention.

FIG. 1B is a schematic cross section of a flip-chip organic lightemitting structure, according to the present invention, after theelectrode structure and the organic structure have been flippedtogether.

FIG. 2 is a schematic cross section of a flip-chip organic lightemitting array, according to the present invention.

FIG. 3A is a schematic bottom-view of a first substrate with electrodestructure and a spacer, according to the present invention.

FIG. 3B is a schematic bottom-view of a first substrate with anelectrode (referred to as electrode structure) and another spacer,according to the present invention.

FIG. 3C is a schematic cross section of a first substrate and secondsubstrate with female and male spacers, according to the presentinvention.

FIG. 4 is a schematic cross section of a flip-chip organic lightemitting array, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to fabricate an ideal organic opto-electronic device (such asan OLED) based on optimized materials and characterized by an enhanceddevice performance and stability, we propose a novel fabricationprocess, herein referred to as flip-chip process. In contrast to acommonly used device fabrication process, where the individual layers(e.g. an anode, organic stack, and a cathode) are deposited subsequentlyon a substrate, the flip-chip process splits off the device fabricationprocess onto different substrates and therefore separates the crucialfabrication processes. As addressed in the introductory portion, theseprocesses often are the deposition process of the electrodes andelectrode modifications. In order to avoid damage of the devicestructure during alignment and fabrication, and to ensure appropriateoperation of the device, spacers are integrated on at least onesubstrate.

Turning now to FIGS. 1A and 1B, a first embodiment of the presentinvention is described. This first embodiment comprises a firstsubstrate 11 carrying an electrode 12 and two spacer halves 13. Thefirst substrate 11 together with the electrode 12 are herein referred toas electrode structure. Corresponding spacer halves 15 are formed on asecond substrate 16. This second substrate 16 also comprises an organicstack 14 (herein referred to as organic structure) and a commonelectrode 17. Such an organic stack at least comprises a light emittinglayer where light is generated if an appropriate voltage is appliedacross the electrodes. The flip-chip organic light emitting device 10 isshown in assembled form in FIG. 1B. The two substrates 11 and 16 areflipped together such that an intimate contact is provided between theelectrode 12 and the organic stack 14. The spacer halves 13 and 15 setthe distance (D) between the two substrates 11 and 16. Furthermore,these spacers precisely define the forces (pressure and stress) actingupon the electrode 12 and the organic stack 14.

The substrate 16 may be a glass substrate for example. Any othertransparent substrate can be chosen as well. The organic stack 14comprises a transparent electrode 17. Well suited as transparentelectrode 17 is ITO, which then acts as anode. The thickness of theanode 17 is chosen to provide as high a conductance as possible. Wellsuited is a thickness of 100 nm or more. In the present embodiment theanode 17 is 100 nm thick. Right on top of the anode 17 there is at leastone organic layer in which electroluminescence takes place if anappropriate voltage is applied. Such an organic layer is usuallyreferred to as organic emission layer (EML).

A cathode 12 is formed on the substrate 11. In the present embodimentsilicon serves as substrate 11. As cathode material a low work functionmetal or alloy, for example Mg/Ag, is used. The thickness of the cathode12 is chosen to provide a high conductance. Well suited is a thicknessof 100 nm or more. In the present embodiment the Mg/Ag cathode 12 is 500nm thick.

Exemplary details of the first embodiment are given in the followingtable.

Layer No. Material Width present example substrate 16 glass 0.05 mm-5 mm 2 mm anode 17 ITO 10-2000 nm 100 nm EL 14 Alq3 10-2000 nm  80 nmcathode 12 Mg/Ag 10-1000 nm 500 nm substrate 11 silicon 0.1 mm-5 mm  1mm

Please note that the first embodiment is a cathode-up structure wherelight 18 is emitted through the anode 17 and substrate 16 into thehalf-space below the device 10, as indicated in FIG. 1B.

The spacers 13 and 15 comprise silicon nitride, SiN_(x), SiO_(x), SiO₂,Siliconoxynitride (SiON), organic compounds such as polyimides,aluminiumoxide, aluminiumnitride, or titaniumoxide, for example. Thecombined thickness (D) of the two spacer halves has to be slightly lessthan the thickness D1 of the organic stack 14 and anode 17 and thethickness D2 of the electrode structure 12 together. As a rule of thumb,D has to be between 80% and 100% of D1+D2. Preferably, the thickness Dis between 90% and 98% of D1+D2. Please note that in the presentembodiment the spacer halves 15 are thicker than the organic stack 14and anode 17. This has the advantage that the stack 14 is protected frombeing mechanically damaged while handling the substrate 16. Thethickness of the spacers depends on the morphological properties of theorganic stack 14 and electrode 12 and can be adapted to achieve the bestresults. It is important that the spacers are non-conducting to preventshorts. If needed, special spacers can be added that provide for aconductive connection between circuitry of the organic structure andcircuitry on the electrode structure. The spacers can be large (wide andlong) if space permits. In OLED display applications, however, insteadof large spacers smaller spacers are preferred. Every pixel of a displaymight be protected by a very small spacer. Thus, extremely robust, largearea and high resolution displays can be fabricated with the inventiveflip-chip approach.

For a proper function of a device according to the present invention,the quality of interface between the two flip-chip parts, is of crucialimportance. It has been demonstrated by the inventors that the interfacebetween the two flip-chip parts can be stabilized, optimized andtailored by applying a special interface formation procedure. Thisprocedure can consist of a simple heating process, or an exposure tointense light, or an UV curing process, or a combination of any of thesemethods. Common to all these procedures is that they lead in combinationwith the present spacers to a homogeneous and uniform interfaceformation. A further advantage of the described interface formationprocess is, that it can be applied to any type of organic/organic,organic/inorganic, and inorganic/inorganic interfaces.

A few examples of the special interface formation procedure are given inthe following. In the case of polymeric systems the application of UVlight can lead to crosslinking between polymers of the two parts of theflip-chip device. In the case of a heat treatment (polymers, smallmolecule systems) the interface is warmed up for some time. The actualheating time as well as the temperature depends on parameters like thechemical structure of the material supposed to form an interface, andthe desired depth of the interface formation process (e.g. is theinterface formation supposed to be limited the immediate neighborhood ofthe two flip-chip parts, or is the interface formation supposed toextend into the two flip-chip parts). The heating time can vary frommuch less than a second up to several hours and more. The interfaceformation temperature is also system dependent. In the case of organicand/or amorphous materials it should not exceed the glass transitiontemperature of the most sensitive layer of the flip-chip structure for along time. For stable glass forming systems, however, it can even behigher.

The spacers, according to the present invention, allow for theapplication of a pressure between the two flip-chip parts withoutrunning the risk to damage the device. One might even apply an externalforce to increase the pressure between the two flip-chip parts. Thepressure also has an impact on the interface formation process.

The present interface formation process allows to form a chemically,morphologically, mechanically and electrically stable interface.

In order to improve the interface formation process, one might apply oneor several special layers on the respective surfaces of the twoflip-chip parts such that a reaction can take place or can be initiatedwhen combining the two halves.

Due to the fact that the spacers define the distance D between the firstand second substrates, also flexible substrates can be employed. Thisallows to realize flexible organic light emitting displays and solarcells where the operation of the individual OLEDs or the individualcells of the solar cell are not influenced when bending the whole devicebecause the spacers provide small independent cells inside the device.The geometry of these cells remains almost unchanged when bending theinventive device.

If silicon is used as first substrate, micro-mechanical techniques canbe employed to define the spacers. Examples of complicated spacers areillustrated in FIGS. 3A-3C. A bottom-view of a first substrate 31 isgiven in FIG. 3A. The substrate 31 carries an electrode 32 and a set ofspacers 33 arranged around the electrode 32. A bottom-view of a firstsubstrate 41 is given in FIG. 3B. This substrate also carries anelectrode 42 and a spacer 43. The spacer 43 forms a rectangular wallaround the electrode 42. Instead of a rectangular wall, any kind of awall like structure may serve as spacer. Well suited for example arehoneycomb structures. If using micro-mechanical techniques there arealmost no bounds to the shape and/or arrangement of spacers.

A cross-sectional view of two spacer halves 53 and 55 is shown in FIG.3C. The upper spacer 53 is formed on the first substrate 51 which alsocarries an electrode (not shown). This upper spacer 53 is a so-calledfemale spacer which has a bay to receive the corresponding counterpartspacer 55 (male spacer). The male spacer 55 is formed on the secondsubstrate 56 on which the organic stack and an electrode is situated(not shown). This kind of an arrangement and equivalent kinds of spacerstructures allow a precise alignment of the first and second substrates51 and 56 if flipped together.

It is to be noted that the spacers can also be formed separately. Onemight for example form a first electrode on a first substrate and growan organic stack on this electrode. Another electrode may be formed on asecond substrate. In addition, a spacer mesh or web (e.g. a honeycombstructure) can be formed separately. Then the spacer mesh or web isplaced on one of the two structures before they are joined together.Such a spacer mesh or web can be made using micro-mechanical techniquesor molding techniques, for example.

In the simplest case the spacers consist of robust, non-conductingmaterials like silicon nitride, SiN_(x), SiO_(x), SiO₂,Siliconoxynitride (SiON), organic compounds such as polyimides,aluminiumoxide, aluminiumnitride, or titaniumoxide, for example. Thesematerials can easily be deposited on the structures and patterned. Theshape of the spacers depends on the actual task, for example for displayapplication the fill factor is a crucial point. Thus the size of thespacers should not exceed 20% of the actual active area. The shape ofthe spacers can be adapted to the special application. For someapplications a self-aligning geometry consisting of a male and a femalespacer part is of advantage.

If necessary for adequate lateral conductivity, an additional layer orstack of layers could be deposited on top of the cathode 12 to improvethe electron injection into the cathode. Note that the electrodestructure might either carry a simple one-layer electrode, a compoundmetal electrode, or a multi-layer electrode. Even certain organic layersmight be part of the electrode structure. The anode 17 might also be asimple one-layer electrode, a compound metal electrode, or a multi-layerelectrode.

Usually, the organic stack comprises several layers. Please note thatthe layered structure of the organic stack is not shown in FIGS. 1A and1B.

When referring to the ‘first substrate’, substrates are meant that aresuited to carry an electrode. Silicon is an example for such asubstrate. Silicon has the advantage that driving circuitry can beintegrated such that complex driving schemes can be realized.

If light is to be emitted through the first substrate the following twoconditions have to be met. First, the electrode carried by the firstsubstrate has to be semitransparent or transparent. Second, thesubstrate has to be semitransparent or transparent, too.

When using the expression ‘second substrate’, any substrate is meantwhich is suited to carry an electrode 17 and at least organic layersuited for light emission (EML) 14. If light is to be emitted throughthe substrate 16, this substrate 16 as well as the electrode 17 have tobe semitransparent or transparent.

It is to be noted that also both substrates might be transparent.

When using the expression ‘electrode’, any kind of a structure isreferred to which is suited to inject carriers (electrons or holes) intoan organic stack. The electrode structure may comprise some organiclayers in addition to the mere electrode material. E.g., a transportlayer may be formed on a metal electrode. The electrode structure may beoptimized by plasma-, UV-, or ozone-treatments, heat and surfacemodifications, polishing and the like to achieve the best materials andthe most stable electrodes.

Another embodiment of the present invention is illustrated in FIG. 2.The shown device 20 is an anode-up array. From the glass substrate 26 upthe array comprises a cathode 27 and an organic stack 24. To be moreprecise, the substrate 26 carries (listed in the order of deposition)ITO/TiN/ETL/EL/HTL. Please note that light is emitted from the activeregion within the organic stack 24 through the metal-compound cathodeand ITO (together referred to as cathode 27) and substrate 26. Pleasenote that in the present embodiment the organic stack 24 comprises anelectron transport layer (ETL), an electroluminescent layer (EL), and ahole transport layer (HTL). In the following, exemplary details of thesecond embodiment are specified. In the present embodiment, thesubstrate 21 just carries the anode 22.

Layer No. Material Width present example substrate 26 glass 0.05 mm-5 mm 3 mm outer cathode 27 ITO 10-2000 nm 20 nm cathode 27 TiN 10-100 nm 40nm ETL and EL 24 Alq3 10-1000 nm 80 nm HTL 24 NPB 5-500 nm 50 nm anode22 Ni 10-2000 nm 50 nm substrate 21 silicon 0.1 mm-5 mm  1 mm

As mentioned, the silicon substrate 21 can be fabricated to containactive Si devices, such as for example an active matrix, drivers, memoryand so forth. Such a silicon substrate 21 with integrated circuits canbe used to realize inexpensive small area organic displays with highresolution and performance as well as large area displays, for example.

The substrate 21 carries spacers 23 and the substrate 26 carries spacers25 which together define the distance between the upper flip-chip partand the lower flip-chip part when both parts of the device 20 are puttogether. The interface between the first (upper) flip-chip part and thesecond (lower) flip-chip part is stabilized by an appropriate interfaceformation process. In the present example this interface is an interfacebetween the Ni anode 22 and the NPB hole transport layer 24.

On top of Si integrated circuits, stable electrodes can be formed. Wellsuited for example are ITO, Al, Cu, Au, Pt, Ni, and Cr. These electrodes22 (which are part of the electrode structure) together with theopposite electrode 27 formed underneath the organic stack 24 are used todrive the organic stack 24 by applying a voltage. The cross-section ofFIG. 2 shows five OLEDs arranged as an array. These OLEDs may be anycolor including blue or white.

Note that the electrode layer 27 can be a continuous layer such thatseveral adjacent OLEDs share a common electrode. The electrode layer canconsist of a combination of various cathode materials, for examplecontaining ITO, TiN, low workfunction metals and alloys - as shown inthe present example.

The organic stacks of the present devices may comprise:

at least one organic emission layers (EML), and

hole transport layer(s) (HTLs); and/or

electron transport layer(s) (ETLs); and/or

inorganic injection/banier/confinement layers; and/or

buffer layers.

TiN and the other metals can be deposited by a variety of techniques,including vacuum evaporation, E-beam evaporation, reactive sputtering,glow discharges, and chemical vapor deposition (CVD). The highertemperature CVD processes can be used because the electrode structure ismade separately from the sensitive organic stack. CVD is not suited forthe fabrication of conventional OLEDs. Vacuum evaporation, E-beamevaporation, reactive sputtering, and glow discharges process are wellsuited for the formation of electrodes. No care has to be taken whenforming the electrode structure about thermal stability and low glasstransition temperatures of the organic materials, sputter damage andthermal stress in the layers of the organic stack.

Yet another embodiment of the present invention is described inconnection with FIG. 4. As shown in this figure, the organicopto-electronic device 60 (an organic R, G, B color display) comprisestwo halves 61 and 62. In the present embodiment, the upper half 61carries male spacers 63 and the lower half 62 carries female spacers 64.It is one purpose of these spacers (like in the other embodiments) todefine the distance between the two halves 61 and 62. It is anotherpurpose of the spacers to form walls within the plane of the two halvesthat define the pixel size and shape. The reason why the spacers aredesigned to form walls is best understood when describing the method ofmaking such the organic opto-electronic device 60.

As described in connection with the other embodiments, the individualhalves of the organic color display 60 are fabricated separately, toallow optimization of the various processing steps. As shown in FIG. 4,the lower half 62 comprises silicon 68 with integrated circuitry (notshown) to drive the pixels. After the formation of the spacers, thepixels are filled with suitable materials 65-67 of different color (e.g.R, G, B). Due to the spacers serving as walls any intermixing of thedifferent materials 65-67 (for example polymers) is avoided. In thepresent example, the pixels of the upper half 61 comprises polymers 69.To obtain a complete R, G, B display, the two halves 61 and 62 have tobe aligned and put together. Optimum performance is achieved by aspecial interface formation procedure. Well suited in the presentexample is a heat treatment to facilitate the formation of a properinterface between the color pixels 65-67 and the polymer 69. The upperhalf 61 carries a common ITO electrode 70 whereas each pixel on thelower half 62 has an individual electrode 71-73 which allows to turnthem on and off individually. These individual electrodes 71-73 areconnected to the above-mentioned appropriate driving circuitry. If anappropriate voltage is applied to the pixels, then the pixel 65 emitsred light, the pixel 66 emits green light, and the pixel 67 emits bluelight. As described before, the spacers can provide conductiveconnections between circuitry on the two halves.

This is especially important for large area displays where theconductivity of the common electrode limits the device performance.

An ink-jet technique can be used to fill the individual pixels. Anink-jet device has a droplet generator with nozzle from which inkdroplets are emitted and directed to the respective pixel on the lowerhalf 62. The ink-jet device or the lower half 62 may be transported at arelatively high speed so that one pixel after the other is filled withthe appropriate color. Also the polymer 69 on the other half 61 can befilled using an ink-jet device.

The present invention allows the use of up to now not yet consideredelectrode materials. Well suited as electrode (cathode) material aremetal-compounds with low workfunction. Metal-compound in the presentcontext stands for any carbide, nitride, or boride of the earlytransition metals (such as group 4 and 5 transition metals) andlanthanides. One example of such a metal-compound is titanium nitride(TiN). These metal-compounds make up a whole new class oflow-workfunction, semi-transparent, conducting materials very wellsuited as cathode for organic devices. Metal-compounds are described andclaimed in a related patent application with Application Serial No.PCT/IB97/01565, entitled “Compound-Metal Contacts for Organic Devicesand Method for Making the Same” filed on Dec. 15, 1997, presentlyassigned to the assignee of the instant application.

Also well suited as electrode material is GaN and other non-degenerate,wide-bandgap semiconductors (nd-WBS). These nd-WBS electrode materialsare addressed in the international patent application WO98/07202 withtitle “Gallium Nitride Based Cathodes for Organic ElectroluminescentDevices and Displays”. The international publication date of this patentapplication is Feb. 19, 1998. All nd-WBSs have the advantage that theirwide bandgap makes them transparent.

Since both ‘halves’ of the organic light emitting devices are formedseparately, even polymers can now be used in connection with evaporatedsmall molecule systems, which was not conceivable so far because of theincompatibility of these two systems (for example polyaniline,polythiophene (derivatives) as hole injecting materials and PPV and PPVderivatives as emitting materials).

In the following some examples of the different organic materials whichcan be used are given.

Electron Transport/Emitting Materials:

Alq₃, Gaq₃, Inq₃, Scq₃, (q refers to 8-hydroxyquinolate or it'sderivatives) and other 8-hydroxyquinoline metal complexes such as Znq₂,Beq₂, Mgq₂, ZnMq₂, BeMq₂, BAlq, and AlPrq₃, for example. These materialscan be used as the ETL or emission layer.

Other classes of electron transporting materials are electron-deficientnitrogen-containing systems, for example oxadiazoles like PBD (and manyderivatives), and triazoles, for example TAZ (1,2,4-triazole).

Finally, materials containing quinoline, quinoxaline, cinnoline,phthalazine and quinaziline functionalities are well known for theirelectron transport capabilities.

Other materials are didecyl sexithiophene (DPS6T), bis-triisopropylsilylsexithiophene (2D6T), azomethin-zinc complexes, pyrazine (e.g. BNVP),styrylanthracene derivatives (e.g. BSA-1, BSA-2), non-planardistyrylarylene derivatives, for example DPVBi (see C. Hosokawa and T.Kusumoto, International Symposium on Inorganic and OrganicElectroluminescence 1994, Hamamatsu, 42), cyano-substituted polymerssuch as cyano-PPV (PPV means poly(p-phenylenevinylene)) and cyano-PPVderivatives.

These functional groups can also be incorporated in polymers, starburstand spiro compounds. Further classes are materials containing pyridine,pyrimidine, pyrazine and pyridazine functionalities.

The following materials are particularly well suited as

Emission Layers and Dopants:

Anthracene, pyridine derivatives (e.g. ATP), Azomethin-zinc complexes,pyrazine (e.g. BNVP), styrylanthracene derivatives (e.g. BSA-1, BSA-2),Coronene, Coumarin, DCM compounds (DCM1, DCM2), distyryl arylenederivatives (DSA), alkyl-substituted distyrylbenzene derivatives (DSB),benzimidazole derivatives (e.g. NBI), naphthostyrylamine derivatives(e.g. NSD), oxadiazole derivatives (e.g. OXD, OXD-1, OXD-7),N,N,N′,N′-tetrakis(m-methylphenyl)-1,3-diaminobenzene (PDA), peryleneand perylene derivatives, phenyl-substituted cyclopentadienederivatives, 12-phthaloperinone sexithiophene (6T), polythiophenes,quinacridones (QA) (see T. Wakimoto et al., International Symposium onInorganic and Organic Electroluminescence, 1994, Hamamatsu, 77), andsubstituted quinacridones (MQA), rubrene, DCJT (see for example: C.Tang, SID Conference San Diego; Proceedings, 1996, 181), conjugated andnon-conjugated polymers, for example PPV and PPV derivatives, dialkoxyand dialkyl PPV derivatives, for example MEH-PPV(poly(2-methoxy)-5-(2′-ethylhexoxy)-1,4-phenylene-vinylene),poly(2,4-bis(cholestanoxyl)-1,4-phenylene-vinylene) (BCHA-PPV), andsegmented PPVs (see for example: E. Staring in International Symposiumon Inorganic and Organic Electroluminescence, 1994, Hamamatsu, 48, andT. Oshino et al. in Sumitomo Chemicals, 1995 monthly report).

Hole Transport Layers and Hole Injection Layers:

The following materials are suited as hole injection layers and holetransport layers. Materials containing aromatic amino groups, liketetraphenyldiaminodiphenyl (TPD-1, TPD-2, or TAD) and NPB (see C. Tang,SID Meeting San Diego, 1996, and C. Adachi et al. Applied PhysicsLetters, Vol. 66, p. 2679, 1995), TPA, NIPC, TPM, DEH (for theabbreviations see for example: P. Borsenberger and D.S. Weiss, OrganicPhotoreceptors for Imaging Systems, Marcel Dekker, 1993). These aromaticamino groups can also be incorporated in polymers, starburst (forexample: TCTA, m-MTDATA, see Y. Kuwabara et al., Advanced Materials, 6,p. 677, 1994, Y. Shirota et al., Applied Physics Letters, Vol. 65, p.807, 1994) and spiro compounds.

Further examples are: Copper(II) phthalocyanine (CuPc),(N,N′-diphenyl-N,N′-bis-(4-phenylphenyl)-1,1′-biphenyl-4,4′-diamine),distyryl arylene derivatives (DSA), naphthalene, naphthostyrylaminederivatives (e.g. NSD), quinacridone (QA), poly(3-methylthiophene)(P3MT) and its derivatives, perylene and perylene derivatives,polythiophene (PT), 3,4,9, 10-perylenetetracarboxylic dianhydride(PTCDA), PPV and some PPV derivatives, for example MEH-PPV,poly(9-vinylcarbazole) (PVK), discotic liquid crystal materials (HPT).

There are many other organic materials known as being good lightemitters, charge transport materials, and charge injection materials,and many more will be discovered. These materials can be used as wellfor making light emitting structures according to the present invention.More information on organic materials can be found in text books andother well known publications, such as the book “Inorganic and OrganicElectroluminescence”, edited by R. H. Mauch et al., Wissenschaft andTechnik Verlag, Berlin, Germany, 1996, and the book “1996 SIDInternational Symposium, Digest of Technical Papers”, first edition,Vol. XXVII, May 1996, published by Society for Information Display, 1526Brookhollow Dr., Suite 82, Santa Ana, Calif., USA.

Additionally, blend (i.e. guest-host) systems containing active groupsin a polymeric binder are also possible. The concepts employed in thedesign of organic materials for OLED applications are to a large extentderived from the extensive existing experience in organicphotoreceptors. A brief overview of some organic materials used in thefabrication of organic photoreceptors is found in the above mentionedpublication of P. Brosenberger and D. S. Weiss, and in Teltech,Technology Dossier Service, Organic Electroluminescence (1995), as wellas in the primary literature.

OLEDs have been demonstrated using polymeric, oligomeric and smallorganic molecules. The devices formed from each type of molecule aresimilar in function, although the deposition of the layers varieswidely. The present invention is equally valid in all forms describedabove for organic light emitting devices based on polymers, oligomers,or small molecules, as well as starburst and Spiro compounds.

Small molecule devices are routinely made by vacuum evaporation.

Evaporation can be performed in a Bell jar type chamber withindependently controlled resistive and electron-beam heating of sources.It can also be performed in a molecular beam deposition systemincorporating multiple effusion cells and sputter sources. Oligomericand polymeric organics can also be deposited by evaporation of theirmonomeric components with later polymerization via heating or plasmaexcitation at the substrate. It is therefore possible to co-polymerizeor create mixtures by co-evaporation.

In general, polymer containing devices (single layer, multilayer,polymer blend systems, etc.) are made by dissolving the polymer in asolvent and spreading it over the substrate either by spin coating orthe doctor blade technique. With our novel method we are able tofabricate now well defined multilayer structures (i.e. with at least twolayers) even with materials which dissolve only in the same solvent.

Additionally, hybrid devices containing both polymeric and evaporatedsmall organic molecules are possible. In this case, the polymer film isgenerally deposited first, since evaporated small molecule layers oftencannot withstand much solvent processing. According to the presentinvention, one is now much more flexible as far as the sequence ofdeposition is concerned.

More interesting is the possibility of making a polymer/inorganictransport layer on top of which monomeric layers are evaporated,possibly also incorporating alloys. If the polymer is handled in aninert atmosphere prior to introduction to vacuum, sufficient cleanlinessfor device fabrication is maintained.

What is claimed is:
 1. A method for making an organic opto-electronicdevice comprising a first flip-chip part with a first substrate and afirst electrode and a second flip-chip part with a second substrate anda second electrode which carries an organic stack, the method comprisingthe steps: forming the first electrode on the first substrate, formingthe second electrode on the second substrate, forming the organic stackon the second electrode, forming spacers of thickness D, with D=k(D1+D2)and 0.5≦k<1, flipping the first substrate and the second substratetogether such that the organic stack is sandwiched between the firstelectrode and the second electrode, and such that a minimum distance Dis kept between the two substrates by the spacers, and applying aninterface formation process to form a stabilized interface between thefirst flip-chip part and the second flip-chip part.
 2. The method ofclaim 1, wherein the parameter k is not less than 0.9 and not greaterthan 0.98.
 3. The method of claim 1, wherein the spacers are formed onone of the two substrates.
 4. The method of claim 1, wherein part of thespacers are formed on the first substrate and corresponding parts areformed on the second substrate.
 5. The method of claim 1, wherein thespacers are formed by using micro-mechanical techniques.
 6. The methodof claim 1, wherein the first substrate with first electrode and/or thesecond substrate with second electrode and organic stack are testedbefore carrying out the step of flipping the first substrate and secondsubstrate together.
 7. The method of claim 1, wherein the firstelectrode is formed on the first substrate using processes which are notcompatible with the organic materials used in the organic stack.
 8. Themethod of claim 1, wherein the first electrode is formed on the firstsubstrate using high temperature processes.
 9. The method of claim 1,wherein the interface formation process is either a heat treatment or aUV treatment.
 10. The method of claim 1, wherein the spacers form wallsdefining individual pixels.
 11. The method of claim 10, wherein thepixels are filled with color emitting material by using an ink-jettechnique.